In efforts to reduce the labor intensive, time consuming screeding of paving materials, numerous types of machines for accomplishing the screeding operation have been developed. Examples of such machines are shown in U.S. Pat. Nos. 1,584,385; 2,426,702; 2,687,679; 3,377,933; 4,115,976; 4,747,726; and in the aforementioned application Ser. No. 356,260 of which this application is a continuation-in-part. In general, these machines comprise a frame supported by two or more rollers, at least one of which is driven, that roll on forms straddling the surface area to be paved and which serve as track or support rails for the machine. A screed roller is located forward on the frame and its axis of rotation is slightly elevated above the axes of the support rollers, so that the screed roller itself is elevated slightly above the support rollers and the forms. The screed roller is generally driven in a reverse direction to that of the support rollers so that as the machine advances through the paving material, which has been dumped between the forms, the screed roller flings and spreads the material ahead of the machine, flattening and leveling the piles thereof into a rough surface. The support rollers then pass over the material, further flattening and smoothing it into a fairly flat, fairly even surface. This surface can be improved by floating or troweling, which is generally done manually by work crews using bull floats or trowels.
In the aforementioned application Ser. No. 356,260, manual troweling or floating is obviated by a finishing roller attachment mounted on the rear of the screeding machine. The finishing roller, which is of smaller diameter than the screeding and support rollers, is rotatably mounted to a pair of support arms, which are pivotally mounted to the machine. Drive means mounted to one of the support arms rotates the finishing roller generally at higher revolutions per minute than the other rollers so that the finishing roller actually slips on the surface of the paving material as the screeding machine is operated. This action causes the soupy material carried in the paving material to rise to the top surface thereof where it is uniformly spread by the finishing roller to produce a highly finished surface. Means are provided for pivoting the support arms so that the finishing roller no longer engages the paving surface, in the event that a highly finished surface is not needed or desired.
While the screeding machines as just described produce an even, smooth, level paved surface, in practice it has been found that when the concrete is poured, air in the form of bubbles and pockets is trapped in the mass. Such air bubbles and pockets tend to reduce the density of the pacing material, weaken the material, and deleteriously effect the finished surface thereof. These effects can be especially damaging where great density and strength of the material is required, such as with airport runways or heavily travelled highways.
Accordingly, it is an object of the invention to provide a screeding machine and method for eliminating, to a large degree, the entrapment of air in poured paving material.
More particularly, it is an object of the present invention to incorporate into the operation of a screeding machine the operation of reducing or eliminating trapped air in the paving material.